Low pressure ballistic system

ABSTRACT

A system for launching a relatively low velocity projectile, which system generates a low pressure propelling gas supply. The propelling gas supply is generated by burning a propellant comprising a small percentage of a primary explosive intimately mixed with a finely divided fuel-oxidizer mixture. The burning rate of the propellant is slower than the detonation rate of the primary explosive, and the propellant sustains burning and generates gas at a rate which is independent of temperature and pressure.

United States Patent [191 Woodring 1 Nov. 13, 1973 LOW PRESSURE BALLISTIC SYSTEM [75] Inventor: William B. Woodring, Stony Creek,

Conn.

[73] Assignee: Olin Corporation, New Haven,

Conn.

[22] Filed: Mar. 10, 1972 [21] Appl. No.:-233,666

[521 U.S. Cl. 102/38 [51] Int. Cl F42b .9/02 [58] Field of Search 102/38, 64, 65, 65.2, 102/45 [56] References Cited UNITED STATES PATENTS 3,120,186 2/1964 Harvey 102/38 3,645,207 2/1972 Daniels 102/45 3,698,319 10/1972 Quinlan et a1. 102/45 3,404,598 10/ l 968 Angelos 3,395,478 7/1968 Harvey 102/40 X Primary Examiner--Rob ert F. Stahl Attorney-Donald R. Motsko et a1.

[57] ABSTRACT A system for launching a relatively low velocity projectile, which system generates a low pressure propelling gas supply. The propelling gas supply is generated by burning a propellant comprising a small percentage of a primary explosive intimately mixed with a finely divided fuel-oxidizer mixture. The burning rate of the propellant is slower than the detonation rate of the primary explosive, and the propellant sustains burning and generates gas at a rate which is independent of temperature and pressure.

6 Claims, 2 Drawing Figures LOW PRESSURE BALLISTIC SYSTEM This invention relates to a low pressure ballistic system for launching relatively low. velocity projectiles such as grenades, cordage-carrying projectiles, and the like.

Various ballistic systems have been devised for launching projectiles at relatively low velocities by using a relatively low pressure supply of propelling gas produced by burning a propellant. Such systems have utilized various conventional smokeless powder propellant charges which have a burning rate, and gas production rate which are dependent on temperature and pressure. Such propellants display a high burning rate and gas production rate at high pressures, and a lower burning rate and gas production rate at lower pressures. For systems designed to launch projectiles at low velocities, for example, cartridge-launched grenades having a velocity of about 250 ft/s'ec, the low pressures of not greater than about 3,000 psi needed to produce this low velocity cannot sustain satisfactory and complete burning of the conventional propellants.

In order to overcome this problem, the prior art has had to devise complex high-low systems within a cartridge for producing combustion gases at the low pressures needed to provide low projectile velocities. In these high-low systems of the prior art, the propellant is burned initially within a small volume in which a sufficiently high pressure is generated to sustain complete burning of the propellant. Once the combustion gases have been generated, they burst out of the initial small volume and into a larger free volume within the cartridge case. Passage into the larger volume reduces the gas pressure accordingly to within the desired range, and exposes the projectile to the reduced gas pressure, whereupon the projectile is launched at the relatively low velocity.

While the prior art high-low systems described above has proven operable, its use places considerable burden on case design due to the necessary inclusion in the cartridge case of a high pressure chamber wherein the propellant can be completely burned. The prior art cartridge casings using this high-low system have necessarily been manufactured from a high strength material such as aluminum, with the high pressure chamber portion of the casing being necessarily sufficiently strong enough to support internal pressures of about 30,000 psi which are needed to promote complete combustion of the smokeless powder propellant. Thus the prior art high-low systems are of complex design and expensive to manufacture, since the less expensive lower strength materials, such as molded or drawn plastics, for example, cannot be used for thecasings.

The ballistic system of this invention provides for the development of a low pressure supply of combustion gases without the use of a high pressure chamber in the cartridge casing. The low pressure gases are supplied by burning a propellant which deflagrates at a steady rate independently of pressure and temperature. Therefore the propellant charge does not have to be confined within a high pressure chamber while it is burned. The combustion gases can be directed immediately when formed into the large volume void within the cartridge casing and brought into contact therein with the projectile. Thus pressure within the cartridge casing never exceeds the required launch pressure, which is relatively low and not greater than about 3,000

psi, for example. The exact launch pressure will vary with projectile weight, desired projectile launch velocity, friction between the projectile and casing, and the like, however, the launch pressure will always be substantially less than the pressure needed to promote complete combustion of the conventional smokeless powder propellants. Since internal pressure developed by the system of this inventionis relatively low, the easing can be formed from a relatively low strength material, such as plastics, or the like. Furthermore, the design of the casing of this invention can be greatly simplified since no high pressure chamber is required. The system of this invention uses a propellant comprising a small percentage of a primary explosive intimately mixed with a finely divided fuel-oxidizer mixture. The burning rate of the propellant is slower than the detonation rate of the primary explosive, and the propellant sustains burning and generates gasat a rate which is independent of temperature and pressure.

It is, therefore, an object of this invention to provide a ballistic system for firing a relatively low velocity projectile.

It is a further object of this invention to provide a system of the character described wherein the internal pressure developed does not exceed the pressure needed to launch the projectile.

It is yet another object of this invention to provide a system of the character described utilizing a propellant which burns and generates gas at :a rate which is independent of pressure and temperature.

It is an additional object of this invention to provide a system of the character described which is inexpensive to manufacture and reliable of operation.

These and other objects, advantages and features of the invention will become more readily apparent from the following detailed description of a preferred embodiment taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevational view of a cartridge formed in accordance with the invention; and

FIG. 2 is a vertical sectional view of a portion of the cartridge of FIG. 1.

Referring to the drawings, there is shown a preferred embodiment of a cartridge 2 formed in accordance with the invention and designed for firing by an impact ignition type firearm. The cartridge 2 includes a casing 4 which can be formed of relatively low strength material, such as plastic, or the like, and a projectile 6, shown in the form of a banded grenade slug. The casing '4 includes a side wall 8 which terminates at one end in an open mouth 10 and which merges at the other end into a transverse, thickened base wall 12. The casing 4 is hollow, with the side wall 8 and base wall 12 providing an internal cavity 14. The projectile 6 is pressed into the mouth 10 of the casing 4 and projects into the cavity 14 to be frictionally held in place by engagement with the side wall 8.

The base wall 12 of the casing is provided with an axial aperture 16 which opens into the cavity 14. A cylindrical plug member 18 is press fitted into the aperture 16, the plug 18 having an internal pocket 20 opening into a flash hole 22, which in turn opens into an enlarged chamber 24 having a restricted mouth 26 which opens into the cavity 14. A conventional battery cup primer assembly 28 is mounted in the plug pocket 20. A moisture barrier foil sheet 30 seals the upper end of the primer assembly 28 to protect the latter against ambient moisture damage. The propellant charge 32 is disposed in the plug chamber 24 and is protected against ambient moisture by moisture barrier foils 34 at its upper and lower boundries. It is noted that between the lower surface of the projectile 6 and the upper surface of the plug 18 and base wall 12, a substantial portion of the cavity 14 remains as a free void within the cartridge.

The propellant 32 is a mixture which burns at a steady rate independently of pressure and temperature. The propellant comprises a mixture pf a primary explosive intimately mixed with a finely divided fuel-oxidizer mixture. By way of example, the propellant can include the following ingredients, given in percentages by weight: a primary explosive such as lead styphnate, stabanate, or the like l50%; a sensitizer such as tetracene 06%; an oxidizer, such as barium nitrate, lead nitrate, potassium chlorate, or the like l060%; a fuel and frictionator, such as antimony sulfide, calcium silicate, or the like 030%; a secondary explosive, such as PETN, TNT, tetryl, cyclonite, or the like 020%; a fuel, such as phosphorus, aluminum, carbon, or the like 30%; and a moderator, such as antimony sulfide, glass, cuprous oxide, or the like 0-30%.

A first propellant was formulated as follows and was tested with the following results observed: the propellant was made up of 40% lead styphnate, 4% tetracene, 30% barium nitrate, antimony sulfide, 6% aluminum, and 5% PETN, all finely divided and intimately admixed to form a homogeneous mixture. This propellant mixture was loaded into a cartridge of the type shown in FIGS. 1 and 2 and having the following specifics. The projectile weighed 0.071 lbs. and was launched through a bore having a cross-sectional area of 0.42 in. and a length of 5 in. A 1.6 grain propellant charge was used and the cartridge case had an initial free volume of 0.31 in. The projectile attained a launch velocity of 246 ft/sec with an internal cartridge pressure of 1,130 psi.

A second propellant formulation was produced as follows and tested with the following results observed. The propellant was made up of 37% lead styphnate, 4% tetracene, 32% barium nitrate, 15% antimony sulfide, 7% aluminum, and 5% PETN, all finely divided and intimately admixed to form a homogeneous mixture. This propellant formulation was loaded into a standard 40 mm grenade cartridge with the following specifications and results. The projectile weighed 0.38 lb. and was launched through a bore having a cross-sectional area of 2.01 in. and a length of 14 in. The average propellant charge used was 10.7 grains with an initial free volume in the cartridge case of 1.47 in. The projectile attained an average launch velocity of 208 ft/sec. with an average internal cartridge pressure of 1,260 psi.

A third propellant formulation was produced as follows' and tested with the following results observed. The propellant formulation consisted of stabanate, 4% tetracene, 46% barium nitrate, 10% anthracite coal, 10% aluminum, and 10% PETN. This propellant formulation was loaded into a standard 40 mm grenade cartridge having a projectile weighing 0.38 lb. and an initial free volume of 1.47 in. The projectile was launched through a bore having a cross-sectional area of 2.01 in. and a length of 14 in. The average propellant charge used was 9.1 grains. The projectile attained an average launch velocity of 217 ft/sec. with an average intemal cartridge pressure of 1,620 psi.

The cartridge shown in FIGS. 1 and 2 operates in the following manner. The cartridge is loaded into the chamber of a specially configured weapon for firing, the weapon being of conventional construction and utilizing a firing pin or hammer. When the weapon is aimed and the trigger pulled, the firing pin or hammer strikes the battery cup primer assembly 28 igniting the priming material therein to create a flame which ruptures the foil layer 30 and passes through the flash hole 22 to rupture the foil 34 and ignite the propellant charge 32. The propellant charge 32 then burns and ruptures the second foil layer 34 to permit combustion gases to pass through the plug mouth 26 and into the free space 14 within the casing/The propellant 32 continues to burn producing combustion gases which flow into the free space 14 progressively increasing the pressure therein. When the pressure within the free space 14 reaches launch proportions (which varies with projectile weight, friction between the projectile and casing, and the like), the projectile 6 is forced out of the casing 4 and propelled through the barrel of the weapon.

Since the velocity of the projectile is relatively low, i.e., not more than about 250 ft/sec., the internal pressure developed within the cartridge is proportionately low. The internal pressure varies with variance of projectile weight, friction, and other variables, but never is permitted to approach 10,000 psi or more, which is required to properly burn conventional smokeless powder propellants. The system of this invention is thus made operable by using a propellant which burns and produces combustion gases at a constant rate independently of pressure and temperature.

Since many changes and variations of the disclosed embodiment of the invention may be made without departing from the inventive concept, it is not intended to limit the invention otherwise than as required by the appended claims.

What is claimed is:

l. A cartridge for launching a projectile at a relatively low velocity, said cartridge comprising:

a. a casing having a transverse end wall and a side wall providing an open-ended mouth;

b. a projectile disposed in said casing and closing off said open-ended mouth, said projectile being spaced apart from said casing end wall so as to provide a free volume within said casing between said end wall and said projectile;

c. propellant charge means within said casing and adjacent to said free volume for propelling said projectile from said casing, said propellant charge means being operative to burn and generate gas into said free volume at a rate which is independent of surrounding pressure; and

d. means for igniting said propellant charge.

2. The cartridge of claim 1, wherein said propellant charge means includes a primary explosive, an oxidizer, and a fuel, and wherein said propellant charge means burns at a rate which is slower than the detonation rate of said primary explosive.

3. The cartridge of claim 2, wherein said primary explosive is selected from the group consisting of lead styphnate and stabanate; said oxidizer is selected from the group consisting of barium nitrate, lead nitrate, and potassium chlorate; and said fuel is selected from the group consisting of phosphorous, aluminum, and carbon.

c. a projectile disposed in said casing and closing off said open-ended mouth, said projectile being spaced apart from said transverse end wall to provide therewith a free volume within said casing;

propellant charge means adjacent said free volume for propelling said projectile from said casing, said propellant charge means being operative to burn and generate gas into said free volume at a rate which is independent of pressure; and

e. means for igniting said propellant charge. 

2. The cartridge of claim 1, wherein said propellant charge means includes a primary explosive, an oxidizer, and a fuel, and wherein said propellant charge means burns at a rate which is slower than the detonation rate of said primary explosive.
 3. The cartridge of claim 2, wherein said primary explosive is selected from the group consisting of lead styphnate and stabanate; said oxidizer is selected from the group consisting of barium nitrate, lead nitrate, and potassium chlorate; and said fuel is selected from the group consisting of phosphorous, aluminum, and carbon.
 4. The cartridge of claim 1, wherein said propellant charge is a homogeneous mixture including 10-50% primary explosive; 10-60% oxidizer; and 5-30% fuel.
 5. The cartridge of claim 1, wherein said propellant charge means is operative to generate a gas pressure within said free volume of no greater than about 3,000 psi to propel said projectile from said casing.
 6. A cartridge for launching a projectile at relatively low velocity, said cartridge comprising: a. a casing having an open-ended mouth; b. means providing a transverse end wall in said casing remote from said mouth; c. a projectile disposed in said casing and closing off said open-ended mouth, said projectile being spaced apart from said transverse end wall to provide therewith a free volume within said casing; propellant charge means adjacent said free volume for propelling said projectile from said casing, said propellant charge means being operative to burn and generate gas into said free volume at a rate which is independent of pressure; and e. means for igniting said propellant charge. 